Paper No. 6
Presentation Time: 9:40 AM
CHARACTER AND IMPLICATIONS OF STORM-BED ICHNOFABRICS: EXAMPLES FROM CRETACEOUS AND TERTIARY ESTUARINE AND SHELF DEPOSITS, EASTERN GULF COASTAL PLAIN
Ichnofabrics in storm-event beds commonly are composite ichnofabrics that record the sequential occupation of substrates by as many as four groups of bioturbators; (1) animals attempting to escape after burial, (2) organisms introduced via storm currents (allochthonous tracemakers), (3) opportunistic organisms that take advantage of newly deposited sediments, and/or (4) fair-weather tracemakers that become established upon resumption of background conditions. Discrimination of ichnofabric elements associated with these groups represents a challenge, particularly where bioturbation by fair-weather organisms is intense, but when achievable can enhance interpretations of event deposition and responses of benthic communities. As illustrated through cases studies of Cretaceous and Tertiary storm-influenced estuarine and marine shelf deposits in the eastern Gulf coastal plain, storm-bed ichnofabrics may be employed to (1) identify discrete event intervals within amalgamated deposits, (2) recognize temporal variations in physical conditions during individual complex events, (3) evaluate relative event magnitudes, which are potentially linked to proximality, (4) assess the extent of post-depositional erosion, and (5) identify organism responses to event-related redistribution of food resources. Beyond supplying information on event-related dynamics, storm-bed ichnofabrics may provide the only clear record of fair-weather infaunal communities, particularly in sequences where ichnofabrics have been preferentially masked by diagenesis.